Advanced driver assistance systems (ADASs) allow information provision through visual, auditory, and haptic signals to achieve multi-dimensional goals of mobility. However, processing information from ADAS requires operating expenses of mental workload that drivers incur from their limited attentional resources. The change in driving condition can modulate driver's workload and potentially impair drive's interaction with ADAS. This paper shows how the measure of cardiac activity (heart rate and the indexes of autonomic nervous system) could discriminate the influence of different driving conditions on driver's workload associated with attentional resources engaged while driving with ADAS. Fourteen drivers performed a car following task with visual ADAS in driving simulator. Driver's workload was manipulated in two conditions: one in monotonous condition (constant speed); and another in more active condition (variable speed). Results showed that driver's workload was similarly affected, but the amount of attentional resources allocation was slightly distinct between both conditions. The analysis of main effect of time demonstrated that drivers' workload increased over time without alterations in autonomic indexes regardless of driving condition. However, the main effect of driving condition produced a higher level of sympathetic activation on variable speed driving compared to driving with constant speed. Variable speed driving requires more adjustment of steering wheel movement to maintain lane-keeping performance, which led to higher level of task involvement and increased task engagement. The proposed measures could help to design new adaptive working modalities for ADAS on the account of variation in driving condition.
